Oxidation of certain heterocyclic compounds



Patented Feb. 23, 19 54 OXIDATION OF CERTAIN HETEROCYCLI COMPOUNDS William G. Toland, Jr., San Rafael, Calif., as-

signor to California Research Corporation, San Francisco, Calif., a corporation of Delaware No Drawing. Application July 23, 1952,

Serial No. 300,519 v 8 Claims. (Cl. 260-437) This invention relates to a process for producing aliphatic carboxylic acids by oxidizing heterocyclic organic compounds.

This application is a continuation-in-part of my copending application Serial No. 216,082, filed March 16, 1951, now abandoned.

It has been found that heterocyclic organic compounds containing 4 to 5 carbon atoms and 1 atom of the group consisting of oxygen and sulfur in the ring can be oxidized to produce monocarboxylic and dicarboxylic aliphatic acids, their amides and/or their salts by heating the heterocyclic compound with sulfur, water and a base to a temperature in the range from 250 to about 700 F. under a superatmospheric pressure sufficient to maintain at least a part of the water in liquid phase. The basic material may be an alkali metal hydroxide, an alkaline earth metal oxide, the salts of alkali or alkaline earth metal hydroxides with weak acids, especially weak inorganic acids, or ammonia. Instead of ammonia itself, ammonium salts and nitrogen compounds convertible to ammonia under the conditions of the reaction may be employed. The variety of sulfur materials and basic materials which may be employed together with water to constitute the oxidizing agent of the process of the invention is indicated in the following table where a number of operative combinations of these materials is listed.

OXIDIZING AGENTS scribed as heterocyclic organic compounds containing either 4 or 5 carbon atoms and 1 or 1 oxygen atom in the ring.

Thiophene, alkyl thiophenes such as methyl thiophene,-dimethyl thiophene, phenyl thiophene,

sulfur and the like, and Z-hydroxythiophene are oxi-' dized by the process of the invention to rupture the ring at the sulfur atom and yield carboxylic acid products. The sulfur atom of thiophene does not appear in the carboxylic acid products and is presumably converted to hydrogen sulfide. Thiophane and its corresponding derivatives are similarly converted to carboxylic acid products.

Furan, furoic acid, furfural, halogenated furans, and furfuryl alcohol are oxidized by the process of the invention to yield carboxylic acid products. During the reaction the ring is opened at the oxygen atom and the oxidative attack occurs at the 2 and 5 positions. Tetrahydrofuran and its derivatives behave similarly to furan and its derivatives under the conditions of the reaction.

The pyrans and thiapyrans are oxidized under the conditions of the reaction undergoing ring rupture at the hetero-atom and the oxidative attack occurring at the 2 and 6positions of the ring.

In order to illustrate the process of the invention, the following examples are provided. The materials subjected to oxidation in the examples are heterocyclic compounds which are readily available in quantities to permit large scale tests and easy identification of the reaction products. The less common heterocyclic compounds mentioned above are oxidized by the process of the invention to yield acidic products, but this work has been done on too small a scale to permit determination of yields.

Ewample 1 This experiment was conducted in a stainless steel bomb having a capacity of 4 liters. The bomb was fitted with a pressure gauge, a thermowell, a bursting disk, a bleed line and valve, and a shaker. The bomb was charged with thiophene and a water solution of ammonium polysulfide. In the composite charge the ratio of thiophene to sulfur to ammonia was 1:2:3. The bomb was sealed and heated to a temperature of 450 F. for a period of 4.3 hours. During the run the pressure attained a maximum value of 1100 p. s. i. g. At the end of the reaction period the bomb was cooled, depressured, and opened. A liquid reaction product mixture was removed from the bomb and stripped with steam to remove ammonia and hydrogen sulfide. At the end of the stripping operation the stripped liquid had a pH of 7. The liquid was filtered to re-, move elemental sulfur. The filtrate was made basic with sodium hydroxide and again stripped with steam to remove ammonia. After stripping with steam the liquid product was reduced in volume by evaporation on a steam bath and acidified with hydrochloric acid to a pH of 2. The acid solution was extracted with ether to remove acetic acid and lower aliphatic mono carboxylic acids and the rafiinate was evaporated to dryness. The dry product was extracted with ethyl alcohol to recover succinic acid. Analysis of the reaction product showed that 57 mol per cent of the thiophene had been converted during the reaction. The yield of succinic acid obtained was 19.2% by weight based on the thiophene converted. The yield of lower aliphatic acids was 17.6% by weight based on thiophene converted.

Example 2 Thiophane was oxidized in the apparatus employed in Example 1. Thiophane, elemental sulfur, and aqueous ammonia were charged to the bomb. The ratio of thiophane to elemental sulfur to ammonium hydroxide was 1 :4:6. The bomb was heated to a temperature of 450 F. for a period of 2 hours. During the reaction period the temperature attained a maximum value of 1050 p. s. i. g. The reaction product was worked up in the mamier described in Example 1. 95.5% of the thiophane was oxidized during the reaction. 19.5% by weight of succinic acid based on thiophane converted was recovered from the reaction product mixture. 9% by weight of acetic acid was also recovered.

Example 3 Tetrahydrofuran was oxidized in the apparatus employed in Example 1. Tetrahydroiuran, elemental sulfur, and aqueous ammonium sulfide were charged to the reactor. The ratio of tetrahydrofuran to sulfur to ammonia contained in the charge was 1:414. The bomb was heated to 450 F. and held at that temperature for a period of 4 hours. During the reaction period the maximum pressure attained was 1500 p. s.'i. g. The reaction product was worked up as in Example 1. All of the tetrahydrofuran was consumed in the reaction. 16.7% by weight of acetic acid based on the tetrahydrofuran charged was recovered from the reaction product. 4.2% of succinic acid was also recovered.

Example 4 Furfural was oxidized in the apparatus employed in Example 1. The bomb was charged with furfural, elemental sulfur, and ammonium sulfide. The weight ratio of furfural to sulfur to ammonia contained in the charge was 125:9. The bomb was heated to 450 F. and held at that temperature for 3 hours. During the reaction period a maximum pressure of 1250 p. s. i. g. was attained. Succinic acid and lower aliphatic acids were contained in the reaction product mixture, but the mixture also contained substantial amounts of resin and tar presumably formed by condensation of the aldehyde.

' When sodium hydroxide, sodium carbonate and calcium carbonate are substituted for ammonia in .runs approximately paralleling those of the above examples, the ultimate reaction products are the same; somewhat lower yields were observed when the carbonates were used.

A study of the operating conditions employed in the process of the invention indicates that oxidation of the heterocycliccompoundsis ordinarily initiated at a temperature of about250" F. and that the reaction may be conducted at temperatures from 250 F. up to the critical temperature of water. Preferably, the reaction is conducted at a temperature in the range from 400 to 600 F. where both reaction rate and process yields are higher than in the remaining portion of the operative range.

In batch operations, such as those illustrated by the above examples, the pressure is ordinarily the autogenous pressure built up in the reaction system and is dependent on the character of the charge and on the reaction temperature employed. Where the heterocyclic compounds are oxidized in a continuous process by passing the reaction mixture through a tubular reactor, a back pressure is maintained which is sufiiciently high to hold a part of the water contained in the charge in liquid phase. Ordinarily, the pres sures will lie in the range from about 500 to 5,000 p. s. 'i. g.

I claim:

1. A method of producing organic acids, their amides and their ammonium salts, which comprises rupturing the heterccyclic ring of a heterocyclic compound containing 4 to 5 carbon atoms and 1 atom of the group consisting of oxygen and sulfur in the ring by heating the heterocyclic compound with elemental sulfur, water and a water-soluble inorganic base to a temperature in the range from 400 F. to 700 F. under a superatmospheric pressure sufiicient to maintain at least a part of the water in liquid phase.

2. A process for producing aliphatic oarboxylic acids which comprises rupturing the heterocyclic ring of a heterocyclic organic compound containing 4 to 5 carbon atoms and 1 atom of the group consisting of oxygen and sulfur by heating the heterocyclic compound with sulfur, water, and a water-soluble inorganic alkaline compound at a temperature in the range from 400 F. to 700 F. under a superatmospheric pressure sufiicient to maintain a part of the water in liquid phase.

3. A process for producing aliphatic carboxylic acids which comprises rupturing the heterocyclic ring of a heterocyclic organic compound containing 4 to 5 carbon atoms and 1 atom or the group consisting of oxygen and sulfur by intimately contacting the heterocyclic compound with sulfur, water, and ammonia at a temperature in the range from 400 F. to 600 F. under a superatmospheric pressure sufiicient to maintain a part of the water in liquid phase.

4. A process for producing aliphatic carboxylic acids which comprises rupturing the heterocyclic ring of a heterocyclic organic compound containing 4 to 5 carbon atoms and 1 atom of the group consisting of oxygen and ulfur by intimately contacting the heterocyclic compound with sulfur, water, and alkali metal hydroxide at a temperature in the range from 400 F. to 600 F. under a superatmospheric pressure sufiicient to maintain a part of the water in liquid phase.

5. A process for producing aliphatic carboxylic acids which comprises rupturing the heterocyclic ring of a heterocyclic organic compound containing 4 to 5 carbon atoms and 1 atom of the group consisting of oxygen and sulfur by intimately contacting the heterocyclic compound with sulfur, water, and alkaline earth metal hydroxide at a temperature in the range from 400 F.Ito 600 F. under a superatmospheric pressure sufficient to maintain a part of the water in liquid phase.

6. Aprocess for producing aliphatic carboxylic acids whichlcomprises rupturing the heterocyclic ring of a heterocyclic organic compound contain ing 4 to 5 carbon atoms and one atom of the group consisting of oxygen and sulfur by intimately contacting the heterocyclic compound with sulfur, water, and a salt of an alkali metal hydroxide and a weak acid at a temperature in the range from 400 F. to 600 F. under a superatmospheric pressure sufiicient to maintain a part of the water in liquid phase.

7. A process for producing aliphatic carboxylic acids which comprises rupturing the heterocyclic ring of a heterocyclic organic compound containing 4 to 5 carbon atoms and one atom of the group consisting of oxygen and sulfur by intimately contacting the heterocyclic compound with sulfur, water, and a salt of an alkaline earth metal and a weak acid at a temperature in the range from 400 F. to 600 F. under 'a superatmospheric pressure sufficient to maintain a part of the water in liquid phase.

8. A process for producing aliphatic carboxylic acids which comprises intimately contacting a heterocyclic organic compound containing 4 to 5 carbon atoms and one atom of the group consisting of oxygen and sulfur with aqueous ammonium polysulfide at a temperature in the range from 400 F. to 700 F. under a superatmospheric pressure suificient to maintain a part of the water in liquid phase.

WILLIAM G. TOLAND, Jaz.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,572,810 Jelinek Oct. 23, 1951 FOREIGN PATENTS Number Country Date 403,123 Germany Sept. 25, 1924 OTHER REFERENCES Adams et al.: "Org. Reactions," vol. 111, pp. 84. 8'1, 91, 92, 103 (1946). 

1. A METHOD OF PRODUCING ORGANIC ACIDS, THEIR AMIDES AND THEIR AMMONIUM SALTS, WHICH COMPRISES RUPTURING THE HETEROCYCLIC RING OF A HETEROCYCLIC COMPOUND CONTAINING 4 TO 5 CARBON ATOMS AND 1 ATOM OF THE GROUP CONSISTING OF OXYGEN AND SULFUR IN THE RING BY HEATING THE HETEROCYCLIC COMPOUND WITH ELEMENTAL SULFUR, WATER AND A WATER-SOLUBLE INORGANIC BASE TO A TEMPERATURE IN THE RANGE FROM 400* F. TO 700* F. UNDER A SUPERATMOSPHERIC PRESSURE SUFFICIENT TO MAINTAIN AT LEAST A PART OF THE WATER IN LIQUIQ PHASE. 